The present invention relates to engine-oil compositions with reduced tendency to form deposits and to the use of alkyl alkoxylates.
According to the prior art as of today, the crank mechanism, piston group, cylinder running path and valve control system of an internal combustion engine are lubricated with an engine oil developed for this particular application. In the closed oil space of the engine, the engine oil, which collects in the oil pan of the engine, is conveyed by delivery pump through an oil filter to the individual lubrication points.
In this system the engine oil has the functions of:
= greater than reducing frictionxe2x80x94reducing wear
= greater than cooling the components
= greater than gastightly sealing the piston from the combustion space
In this connection, the oil is subjected to the following loads during operation:
= greater than contact with hot components (up to higher than 300xc2x0 C.)
= greater than presence of air (oxidation), nitrogen oxides (nitration), fuel and its combustion residues (wall condensation, ingress of material in liquid form) and carbon particles from combustion (ingress of solid foreign substances).
= greater than At the instant of combustion, the oil film on the cylinder is exposed to intense radiated heat.
= greater than The turbulence generated by the crank mechanism of the engine creates a large active surface of the oil in the form of droplets in the gas space of the crank mechanism and gas bubbles in the oil pan.
In the course of engine operation, the listed loads of evaporation, oxidation, nitration, dilution with fuel and ingress of particles change the engine oil itself and components of the engine which are wetted with engine oil during operation. Consequently, the following effects among others occur which are not desired for satisfactory operation of the engine:
1. Change of the viscosity (determined in the low-temperature range at 40 and 100xc2x0 C.)
2. Pumpability of the oil at low outside temperatures
3. Deposit formation on hot and cold components of the engine
This phenomenon includes the development of gummy layers (of brown to black color) all the way to formation of carbon. These deposits impair the function of individual components, such as free movement of the piston rings and constriction of air-conveying components of the turbocharger (diffusor and spirals). Consequently, serious engine damage or power loss is suffered and the exhaust-gas emissions increase.
Furthermore, a spongy deposit layer forms preferentially on the horizontal surfaces of the oil space, and in the extreme case can also clog oil filters and oil ducts of the engine, also leading to engine damage.
4. Reduction of wear protection
To ensure trouble-free engine operation, the engine manufacturers specify a maximum useful life of the engine oil (mileage or service time between oil changes) and require proof of the performance capability of an engine oil in the form of test results of standardized test procedures and engine tests (such as API classification in the USA or ACEA test sequences in Europe). In addition, procedures defined by the manufacturer itself are also used to be able to evaluate engine oil in terms of its suitability.
The reduction of deposit formation and the assurance of greater detergency and dispersion capability over a long useful life is of crucial importance in the foregoing release procedures.